Core-sheath conjugate fiber for artificial hair, hair ornament including same, and method for producing same

ABSTRACT

One or more embodiments of the present invention relate to a core-sheath conjugate fiber for artificial hair including a core and a sheath. The core is composed of a polyester-based resin composition containing a polyester-based resin as a main component, and the sheath is composed of a polyamide-based resin composition containing a polyamide-based resin as a main component. A core-to-sheath area ratio of the core to the sheath is 2:8 to 7:3, and both a fiber cross-section and a core cross-section have a flat shape, a major axis of the core cross-section is in a direction that substantially coincides with a direction of a major axis of the fiber cross-section, and an eccentricity ratio of the fiber in a minor axis direction is 5% or more. As a result, fibers for artificial hair having a texture and an appearance that are similar to those of human hair and having favorable curl setting properties are provided.

TECHNICAL FIELD

One or more embodiments of the present invention relate to core-sheathconjugate fibers for artificial hair that can be used as an alternativeto human hair, hair ornaments including the core-sheath conjugate fibersfor artificial hair, and a method for producing the core-sheathconjugate fibers for artificial hair.

BACKGROUND ART

Human hair has conventionally been used for hair ornaments such ashairpieces, hair wigs, hair extensions, hair bands, and doll hair.However, in recent years, it has become difficult to obtain human hair.For this reason, there is a growing demand for artificial hair that canreplace human hair. Examples of a material of artificial hair includesynthetic fibers such as acrylic fibers, vinyl chloride fibers,vinylidene chloride fibers, polyester fibers, polyamide fibers, andpolyolefin fibers. Patent Document 1 discloses, as a fiber forartificial hair, a core-sheath conjugate fiber in which apolyester-based resin is a core component and a polyamide-based resin isa sheath component, for example. Patent Document 1 discloses that in amelt spinning method, polyethylene terephthalate with a high degree ofpolymerization and polyamide with a high degree of polymerization areused, rapidly solidified through liquid cooling, allowed to pass througha fiber surface layer crystallization facilitating device to provide aspecific stripe-shaped uneven structure to the fiber surface, andthereby it is possible to obtain a fiber for artificial hair in whichthe strength of the fiber is ensured, and the gloss of the polyamide ofthe sheath is suppressed, and that has a feel similar to that of humanhair, and has high durability and heat resistance.

Meanwhile, artificial hair is required to also have curl settingproperties and curl-holding properties. Attempts have been made toimprove these properties by controlling the material and cross-sectionalshape of the fiber. Patent Document 2 discloses that it is possible toobtain a core-sheath conjugate fiber for artificial hair that includes acore and a sheath, in which a major axis of a core cross-section is in adirection that substantially coincides with a direction of a major axisof a fiber cross-section, and an eccentricity in the major axisdirection is 5% or more, thus the core-sheath conjugate fiber forartificial hair having a texture and an appearance similar to those ofhuman hair, having favorable curability without setting curls, andhaving greatly improved curl-holding properties, for example.

CITATION LIST Patent Document

-   [Patent Document 1] JP H3-185103A-   [Patent Document 2] WO 2018/179803A1

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, a fiber for artificial hair in which a polyamide-based resin isused in the sheath as described in Patent Document 1 has a good textureand durability but has a problem of poor curl setting properties. Also,a fiber for artificial hair having a structure eccentric in the majoraxis direction as described in Patent Document 2 has latentcrimpability, and a fiber for artificial hair that has improvedcurl-holding properties can be obtained without setting curls, but thereis a problem of poor curl setting properties when providing curls usinga hair iron or the like.

In order to solve the conventional problems, one or more embodiments ofthe present invention provide fibers for artificial hair that have atexture and an appearance similar to those of human hair and favorablecurl setting properties.

Means for Solving Problem

One or more embodiments of the present invention relate to a core-sheathconjugate fiber for artificial hair that includes a core and a sheath.The core is composed of a polyester-based resin composition containing apolyester-based resin, and the sheath is composed of a polyamide-basedresin composition containing a polyamide-based resin. In the conjugatefiber for artificial hair, a core-to-sheath area ratio of the core tothe sheath is 2:8 to 7:3. Both a fiber cross-section and a corecross-section have a flat shape. A major axis of the core cross-sectionis in a direction that substantially coincides with a direction of amajor axis of the fiber cross-section, and an eccentricity ratio of thefiber in a minor axis direction is 5% or more.

One or more embodiments of the present invention also relate to a hairornament including the core-sheath conjugate fiber for artificial hair.

One or more embodiments of the present invention relate to a method forproducing the core-sheath conjugate fiber for artificial hair, themethod including melt spinning a polyester-based resin composition and apolyamide-based resin composition using a core-sheath conjugate nozzle,in which both a fiber cross-section and a core cross-section of thecore-sheath conjugate fiber for artificial hair have a flat shape, amajor axis of the core cross-section is in a direction thatsubstantially coincides with a direction of a major axis of the fibercross-section, and an eccentricity ratio of the fiber in a minor axisdirection is 5% or more.

Effects of the Invention

One or more embodiments of the present invention can provide core-sheathconjugate fibers for artificial hair that have a texture and anappearance similar to those of human hair, and favorable curl settingproperties, and a hair ornament that includes the core-sheath conjugatefibers for artificial hair.

According to a production method of one or more embodiments of thepresent invention, it is possible to obtain core-sheath conjugate fibersfor artificial hair that have a texture and an appearance similar tothose of human hair, and favorable curl setting properties.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a fiber cross-section of acore-sheath conjugate fiber for artificial hair according to one or moreembodiments of the present invention.

FIG. 2 is a laser microscopic photograph of fiber cross-sections offibers of Example 1.

FIG. 3 is a laser microscopic photograph of fiber cross-sections offibers of Comparative Example 1.

DESCRIPTION OF THE INVENTION

The inventor of the present invention conducted intensive studies inorder to resolve the above issues and found that core-sheath conjugatefibers for artificial hair (also simply referred to as “core-sheathconjugate fibers” in the following) with which poor curl settingproperties which result from use of a polyamide-based resin, can beimproved, that has a texture and an appearance that are similar to thoseof human hair, and has favorable curl setting properties could beobtained as a result of in a core-sheath conjugate fiber for artificialhair that includes a core and a sheath, the core being composed of apolyester-based resin composition containing a polyester-based resin asa main component, the sheath being composed of a polyamide-based resincomposition containing a polyamide-based resin as a main component,setting a core-to-sheath area ratio of the core to the sheath to 2:8 to7:3, forming a fiber cross-sectional shape and a core cross-sectionalshape in a flat shape, setting a major axis of the core cross-section isin a direction that substantially coincides with a direction of a majoraxis of the fiber cross-section, and setting an eccentricity ratio ofthe fiber in a minor axis direction to 5% or more, thus completing thepresent invention.

(Fiber Shape)

The core-sheath conjugate fiber for artificial hair according to one ormore embodiments of the present invention includes a core and a sheath,and a fiber cross-section and a core cross-section have a flat shape.Examples of the flat shape include an elliptical shape, a flatmultilobed shape, and an oval shape. Examples of the flat multilobedshape include a shape in which two or more lobed portions having a shapeselected from the group consisting of a circular shape and an ellipticalshape are connected via recesses. In a flat multilobed shape, a circularand/and elliptical shape partially overlap each other at the connectedportion. The shape of the fiber cross-section is preferably a flatmultilobed shape, and more preferably a flat bilobed shape. Note thatthe shape of the circular or elliptical portions does not absolutelyhave to be a continuous arc, and may also be a substantially ellipticalshape that is partially deformed, as long as no acute angle is formed.Furthermore, no consideration needs to be given to an unevenness with asize of 2 μm or less generated at an outer circumference of the fibercross-section and an outer circumference of the core due to an additiveor the like contained.

It is preferable that, on a fiber cross-section of the core-sheathconjugate fiber for artificial hair according to one or more embodimentsof the present invention, a length of the major axis of the fibercross-section, where the major axis of the fiber cross-section is alongest straight line among an axisymmetric axis and straight linesconnecting any two points on the outer circumference of the fibercross-section so as to be parallel to the axisymmetric axis, and alength of a first minor axis of the fiber cross-section, where the firstminor axis of the fiber cross-section is a longest straight line formedwhen any two points on the outer circumference of the fibercross-section are connected perpendicularly to the major axis of thefiber cross-section, satisfy the equation (1) below.

The length of the major axis of the fiber cross-section/the length ofthe first minor axis of the fiber cross-section=1.1 or more and 2.0 orless  (1)

Further, it is preferable that, on a fiber cross-section, a length ofthe major axis of the core cross-section, where the major axis of thecore cross-section is a longest straight line among an axisymmetric axisand straight lines connecting any two points on the outer circumferenceof the core cross-section so as to be parallel to the axisymmetric axis,and a length of a first minor axis of the core cross-section, where thefirst minor axis of the core cross-section is a longest straight lineformed when any two points on the outer circumference of the corecross-section are connected perpendicularly to the major axis of thecore cross-section, satisfy the equation (2) below.

The length of the major axis of the core cross-section/the length of thefirst minor axis of the core cross-section=1.3 or more and 2.0 orless  (2)

The core-sheath conjugate fiber for artificial hair has a flatmultilobed fiber cross-section, which is a shape in which two or morelobed portions of circular and elliptical are connected via recesses.Thus, because the fiber surface has smooth unevenness, the contact areaof fibers and the contact area with a hair comb when running the haircomb are reduced, and thus a texture similar to that of human hair and afavorable combing property can be realized with ease.

Also, in the core-sheath conjugate fiber for artificial hair, the majoraxis of the core cross-section is in a direction that substantiallycoincides with a direction of the major axis of the fiber cross-section.In one or more embodiments of the present invention, the wording “themajor axis of the core cross-section is in a direction thatsubstantially coincides with a direction of the major axis of the fibercross-section” indicates that an angle formed between the major axis ofthe fiber cross-section and the major axis of the core cross-section isless than 15 degrees. When the major axis of the core cross-section isin a direction that substantially coincides with the direction of themajor axis of the fiber cross-section and a ratio between the length ofthe major axis of the core cross-section to the length of the firstminor axis of the core cross-section is within the above range, on afiber cross-section, the outer circumferential shape of the fibercross-section and the outer circumferential shape of the corecross-section are similar to each other, and thus a good texture and afavorable appearance of the fiber for artificial hair are maintained andit is possible to prevent fiber separation due to coming off of the twocomponents from each other and prevent the core from being exposed fromthe fiber surface. Further, there is also an advantage in molding that anozzle for realizing the above-described cross-sectional shape can beeasily designed because a change from the shape of a fiber extruded fromthe nozzle to the cross-sectional shape of the molded fiber is reduced.Since the major axis of the core cross-section is in a direction thatsubstantially coincides with a direction of the major axis of the fibercross-section, the entire fiber and the core have the same anisotropy ofthe modulus of elasticity in bending resulting from the moment ofinertia of area, and thus it is easy to adjust the quality required forartificial hair, such as a texture and combability.

An eccentricity ratio of the core-sheath conjugate fiber for artificialhair in the minor axis direction is 5% or more, preferably 5% or moreand 50% or less more preferably 6% or more and 40% or less, even morepreferably 10% or more and 30% or less, and further preferably 12% ormore and 25% or less. When a fiber cross-section is flat, the bendingelastic modulus of the fiber is anisotropic in the major and minor axisdirections. When curls are to be set using a hair iron or curling iron,fibers are bent in the minor axis direction in which the fibers have asmall bending elastic modulus, and are heated while being strained. As aresult of setting the eccentricity ratio in the minor axis directionwithin the above range, a larger strain is applied to the resin in thecore compared to a case where fibers have no eccentricity, and the setfibers have strong curls. Also, in the case of fibers that are eccentricin the major axis direction, a torsional moment occurring in a fibercross-section tends to act, and the fibers crimp in an undesireddirection, resulting in an unnatural appearance. On the other hand, inthe case of fibers that are eccentric in the minor axis direction, atorsional moment occurring in a fiber cross-section is reduced andlatent crimpability caused by eccentricity is reduced, compared to acase where fibers are eccentric in the major axis direction. Therefore,it is possible to suppress undesired crimping and realize a naturalappearance.

An eccentricity ratio of the core-sheath conjugate fiber for artificialhair in the minor axis direction can be calculated using the equation(3) below, based on the length of the first minor axis of the fibercross-section and a two-point distance between the center point of thefirst minor axis of the fiber cross-section and the center point of thefirst minor axis of the core cross-section, on a fiber cross-section.The two-point distance between the center point of the first minor axisof the fiber cross-section and the center point of first the minor axisof the core cross-section refers to the distance between a straight linethat passes through the center point of the first minor axis of thefiber cross-section and intersects perpendicularly to the first minoraxis of the fiber cross-section and a straight line that passes throughthe center point of the first minor axis of the core cross-section andintersects perpendicularly to the first minor axis of the corecross-section.

The eccentricity ratio (%) in the minor axial direction=the two-pointdistance between the center point of the first minor axis of the fibercross-section and the center point of the first minor axis of the corecross-section/(length of the first minor axis of the fibercross-section/2)×100  (3)

FIG. 1 is a schematic view showing a fiber cross-section of acore-sheath conjugate fiber for artificial hair according to one or moreembodiments of the present invention. A core-sheath conjugate fiber 1for artificial hair according to an embodiment includes a sheath 10 anda core 20. The core-sheath conjugate fiber 1 for artificial hairaccording to this embodiment has a flat bilobed cross-sectional shape inwhich two elliptical portions are connected via two recesses, and thecore 20 has an elliptical cross-sectional shape. Ina flat bilobed shape,two elliptical portions partially overlap each other at the connectedportion.

In the core-sheath conjugate fiber 1 for artificial hair according tothis embodiment, a length L of a major axis 11 of the fibercross-section and a length S1 of a first minor axis 12 of the fibercross-section preferably satisfy the equation (1), i.e., L/S1 ispreferably 1.1 or more and 2.0 or less.

Further, in the core-sheath conjugate fiber 1 for artificial hairaccording to this embodiment, a length Lc of a major axis 21 of the corecross-section and a length Sc1 of a first minor axis 22 of the corecross-section preferably satisfy the equation (2), i.e., Lc/Sc1 ispreferably 1.3 or more and 2.0 or less.

Also, in the core-sheath conjugate fiber 1 for artificial hair accordingto this embodiment, the eccentricity ratio (%) in the minor axisdirection can be calculated as follows, based on the length S1 of thefirst minor axis of the fiber cross-section and a two-point distance dbetween a center point 13 of the first minor axis 12 of the fibercross-section and a center point 23 of the first minor axis 22 of thecore cross-section (i.e., the distance between the major axis 11 of thefiber cross-section and the major axis 21 of the core cross-section).

Eccentricity ratio in minor axis direction (%)=d/(S1/2)×100

The above-described cross-sectional shapes of the fiber and the core canbe controlled by using a nozzle (pores) with a shape close to the targetcross-sectional shape.

There is no particular limitation on the core cross-sectional shape aslong as the core cross-sectional shape is flat, and the major axis ofthe core cross-section is in a direction that substantially coincideswith the direction of the major axis of the fiber cross-section.However, the ratio of the length of the major axis of the corecross-section and the length of the first minor axis of the corecross-section is preferably within the above range, and the core havingan elliptical cross-sectional shape, a flat multilobed cross-sectionalshape such as a flat bilobed shape, or the like is more preferably used.

The core-to-sheath area ratio of the core to the sheath of thecore-sheath conjugate fiber for artificial hair is 2:8 to 7:3. When thecore-to-sheath area ratio is in this range, a flexural rigidity value,which is a physical property related to a texture, a feel, and the like,is similar to that of human hair, and thus core-sheath conjugate fibersfor artificial hair with a quality similar to that of human hair can beobtained. If the area of the core is smaller than this range, theflexural rigidity value is lower than that in human hair, and thuscore-sheath conjugate fibers for artificial hair with a quality similarto that of human hair cannot be obtained. On the other hand, if the areaof the core is larger than this range, the flexural rigidity value isexcessively large and thus is not similar to that of human hair, and,moreover, the sheath is so thin that the core is likely to be exposed,and the core and the sheath are likely to separate from each other. Fromthe viewpoint of obtaining a texture and a feel that are similar tothose of human hair, the core-to-sheath area ratio of the core to thesheath of the core-sheath conjugate fiber for artificial hair ispreferably 3:7 to 7:3, and more preferably 3:7 to 6:4. In order toprevent separation of the sheath from the core on a fiber cross-sectionof the core-sheath conjugate fiber for artificial hair, it is preferablethat the core is not exposed from the fiber surface and is completelycovered by the sheath.

From the viewpoint of suitability for artificial hair, the core-sheathconjugate fiber for artificial hair has a single fiber fineness ofpreferably 10 dtex or more and 150 dtex or less, more preferably 30 dtexor more and 120 dtex or less, even more preferably 40 dtex or more and100 dtex or less, and even more preferably 50 dtex or more and 90 dtexor less.

When the core-sheath conjugate fibers for artificial hair according toone or more embodiments of the present invention are in the form of anaggregate of fibers, e.g., a fiber bundle, all the fibers do notnecessarily have the same fineness, the same core-to-sheath area ratio,and the same cross-sectional shape, but some of them may have differentfinenesses, different ore-to-sheath area ratios, and cross-sectionalshapes.

In the core-sheath conjugate fiber for artificial hair, the core iscomposed of a polyester-based resin composition containing apolyester-based resin as a main component, and the sheath is composed ofa polyamide-based resin composition containing a polyamide-based resinas a main component.

In one or more embodiments of the present invention, the polyester-basedresin composition containing a polyester-based resin as a main componentindicates that the polyester-based resin composition contains thepolyester-based resin in an amount of more than 50% by weight withrespect to 100% by weight of the total weight of the polyester-basedresin composition, and the content of the polyester-based resin ispreferably 60% by weight or more, more preferably 70% by weight or more,even more preferably 80% by weight or more, further preferably 90% byweight or more, and still more preferably 95% by weight or more.

It is preferable to use, as the polyester-based resin, at least oneselected from the group consisting of polyalkylene terephthalate and acopolyester mainly containing polyalkylene terephthalate. In anembodiment of the present invention, the wording “copolyester mainlycontaining the polyalkylene terephthalate” refers to the copolyestercontaining 80 mol % or more of polyalkylene terephthalate.

Examples of the polyalkylene terephthalate include, but are notparticularly limited to, polyethylene terephthalate, polypropyleneterephthalate, polybutylene terephthalate, and polycyclohexanedimethylene terephthalate.

Examples of the copolyester mainly containing the polyalkyleneterephthalate include, but are not particularly limited to, copolyestersmainly containing polyalkylene terephthalate such as polyethyleneterephthalate, polypropylene terephthalate, polybutylene terephthalate,or polycyclohexane dimethylene terephthalate and other copolymerizablecomponents.

Examples of the other copolymerizable components include: polycarboxylicacids such as isophthalic acid, orthophthalic acid,naphthalenedicarboxylic acid, paraphenylenedicarboxylic acid,trimellitic acid, pyromellitic acid, succinic acid, glutaric acid,adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioicacid, and their derivatives; dicarboxylic acids and their derivativescontaining sulfonates such as 5-sodiumsulfoisophthalic acid anddihydroxyethyl 5-sodiumsulfoisophthalate; 1,2-propanediol;1,3-propanediol; 1,4-butanediol; 1,6-hexanediol; neopentyl glycol;1,4-cyclohexanedimethanol; diethylene glyco; polyethylene glycol;trimethylolpropane; pentaerythritol; 4-hydroxybenzoic acid;ε-caprolactone: and an ethylene glycol ether of bisphenol A.

The copolyester is preferably produced by adding a small amount of othercopolymerizable components to polyalkylene terephthalate serving as amain component, and allowing them to react with each other, from theviewpoint of stability and ease of operation. Examples of thepolyalkylene terephthalate include a polymer of terephthalic acid and/orits derivatives (e.g., methyl terephthalate) and alkylene glycol. Thecopolyester may be produced by adding a small amount of monomer oroligomer component serving as other copolymerizable components, to amixture of terephthalic acid and/or its derivatives (e.g., methylterephthalate) and alkylene glycol, used for polymerization ofpolyalkylene terephthalate serving as a main component, and subjectingthem to polymerization.

It is sufficient that the copolyester has a structure in which the othercopolymerizable components are polycondensed on the main chain and/orside chain of polyalkylene terephthalate serving as a main component,and the copolymerization method and the like are not particularlylimited.

Specific examples of the copolyester mainly containing polyalkyleneterephthalate include a polyester obtained through copolymerization ofpolyethylene terephthalate serving as a main component with one compoundselected from the group consisting of an ethylene glycol ether ofbisphenol A, 1,4-cyclohexanedimethanol, isophthalic acid, anddihydroxyethyl 5-sodiumsulfoisophthalate.

The polyalkylene terephthalate and the copolyester mainly containingpolyalkylene terephthalate may be used individually or in a combinationof two or more. In particular, polyethylene terephthalate; polypropyleneterephthalate; polybutylene terephthalate; a polyester obtained throughcopolymerization of polyethylene terephthalate serving as a maincomponent with an ethylene glycol ether of bisphenol A; a polyesterobtained through copolymerization of polyethylene terephthalate servingas a main component with 1,4-cyclohexanedimethanol; a polyester obtainedthrough copolymerization of polyethylene terephthalate serving as a maincomponent with isophthalic acid; a polyester obtained throughcopolymerization of polyethylene terephthalate serving as a maincomponent with dihydroxyethyl 5-sodiumsulfoisophthalate, and the likeare preferably used individually or in a combination of two or more.

The intrinsic viscosity (also be referred to as an “IV value”) of thepolyester resin is not particularly limited, and is preferably 0.3 dL/gor more and 1.2 dL/g or less, and more preferably 0.4 dL/g or more and1.0 dL/g or less. When the intrinsic viscosity is 0.3 dL/g or more, itis possible to prevent a decrease in the mechanical strength of theresulting fibers, and also to eliminate the risk of dripping during aflammability test. When the intrinsic viscosity is 1.2 dL/g or less, themolecular weight does not become too large and the melt viscosity doesnot become too high, thereby facilitating melt spinning and making thefineness of the fibers more likely to be uniform.

The polyester-based resin composition may contain other resins inaddition to the polyester-based resin. Examples of the other resinsinclude a polyamide-based resin, a vinyl chloride-based resin, amodacrylic-based resin, a polycarbonate-based resin, a polyolefin-basedresin, and a polyphenylene sulfide-based resin. Other resins may be usedindividually or in combinations of two or more.

In one or more embodiments of the present invention, a polyamide-basedresin composition containing a polyamide-based resin as a main componentindicates that the polyamide-based resin composition contains thepolyamide-based resin in an amount of more than 50% by weight withrespect to 100% by weight of the total weight of the polyamide-basedresin composition, and the content of the polyamide-based resin ispreferably 60% by weight or more, more preferably 70% by weight or more,even more preferably 80% by weight or more, further preferably 90% byweight or more, and still more preferably 95% by weight or more.

The polyamide-based resin refers to a nylon resin obtained bypolymerizing at least one selected from the group consisting of lactam,an aminocarboxylic acid, a mixture of a dicarboxylic acid and diamine, amixture of a dicarboxylic acid derivative and diamine, and a salt of adicarboxylic acid and diamine.

Specific examples of the lactam include, but are not particularlylimited to, 2-azetidinone, 2-pyrrolidinone, δ-valerolactam,ε-caprolactam, enantholactam, capryllactam, undecalactam, andlaurolactam. Among them, ε-caprolactam, undecalactam, and laurolactamare preferred, and ε-caprolactam is particularly preferred. Theselactams may be used individually or in combinations of two or more.

Specific examples of the aminocarboxylic acid include, but are notparticularly limited to, 6-aminocaproic acid, 7-aminoheptanoic acid,8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid,11-aminoundecanoic acid, and 12-aminododecanoic acid. Among them,6-aminocaproic acid, 11-aminoundecanoic acid, and 12-aminododecanoicacid are preferred, and 6-aminocaproic acid is particularly preferred.These aminocarboxylic acids may be used individually or in combinationsof two or more.

Specific examples of the dicarboxylic acid, which is used in the mixtureof a dicarboxylic acid and diamine, the mixture of a dicarboxylic acidderivative and diamine, or the salt of a dicarboxylic acid and diamine,include, but are not particularly limited to, the following: aliphaticdicarboxylic acids such as oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid,sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid,tetradecanedioic acid, pentadecanedioic acid, and octadecanedioic acid;alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; andaromatic dicarboxylic acids such as phthalic acid, isophthalic acid,terephthalic acid, and naphthalenedicarboxylic acid. Among them, adipicacid, sebacic acid, dodecanedioic acid, terephthalicacid, andisophthalic acid are preferred, and adipic acid, terephthalic acid, andisophthalic acid are particularly preferred. These dicarboxylic acidsmay be used individually or in combinations of two or more.

Specific examples of the diamine, which is used in the mixture of adicarboxylic acid and diamine, the mixture of a dicarboxylic acidderivative and diamine, or the salt of a dicarboxylic acid and diamine,include, but are not particularly limited to, the following: aliphaticdiamines such as 1,4-diaminobutane, 1,5-diaminopentane,1,6-diaminohexane, 2-methyl-1,5-diaminopentane (MDP),1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane,1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane,1,13-diaminotridecane, 1,14-diaminotetradecane, 1,15-diaminopentadecane,1,16-diaminohexadecane, 1,17-diaminoheptadecane, 1,18-diaminooctadecane,1,19-diaminononadecane, and 1,20-diaminoeicosane; alicyclic diaminessuch as cyclohexanediamine and bis-(4-aminohexyl)methane; and aromaticdiamines such as m-xylylenediamine and p-xylylenediamine. Among them,aliphatic diamines are preferred, and hexamethylenediamine(1,6-diaminohexane) is particularly preferred. These diamines may beused individually or in combinations of two or more.

Examples of the polyamide-based resin (also referred to as nylon resin)include, but are not particularly limited to, nylon 6, nylon 66, nylon11, nylon 12, nylon 6/10, nylon 6/12, semi-aromatic nylons includingunits of nylon 6T and/or nylon 6I, and copolymers of these nylon resins.In particular, nylon 6, nylon 66, and a copolymer of nylon 6 and nylon66 are more preferred.

The polyamide-based resin can be produced by, e.g., a polyamide-basedresin polymerization method that includes heating raw materials for thepolyamide-based resin in the presence or absence of a catalyst. Themethod may or may not include a stirring process during thepolymerization, but it is preferable that the raw materials are stirredto obtain a homogeneous product. The polymerization temperature may beset as appropriate in accordance with the degree of polymerization ofthe target polymer, the reaction yield, and the reaction time, and maybe set to be lower in view of the quality of the polyamide-based resinto be obtained. The reaction rate may also be set as appropriate. Thepressure is not particularly limited, and it is preferable that thepolymerization system is placed under reduced pressure to efficientlyextract volatile components out of the polymerization system.

The ends of the polyamide-based resin used in the present invention maybe capped with an end-capping agent such as a carboxylic acid compoundor an amine compound, if necessary. When a monocarboxylic acid ormonoamine is used as an end-capping agent, the terminal amino groupconcentration or the terminal carboxyl group concentration of theresulting nylon resin is reduced compared to the case where such anend-capping agent is not used. On the other hand, when a dicarboxylicacid or diamine is used as an end-capping agent, the sum of the terminalamino group concentration and the terminal carboxyl group concentrationis unchanged, but the ratio of the terminal amino group concentration tothe terminal carboxyl group concentration is changed.

Specific examples of the carboxylic acid compound include, but are notparticularly limited to, the following: aliphatic monocarboxylic acidssuch as acetic acid, propionic acid, butyric acid, valeric acid, caproicacid, enanthic acid, caprylic acid, pelargonic acid, undecanoic acid,lauric acid, tridecanoic acid, myristic acid, myristoleic acid, palmiticacid, stearic acid, oleic acid, linoleic acid, and arachic acid:alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid andmethylcyclohexanecarboxylic acid; aromatic monocarboxylic acids such asbenzoic acid, toluic acid, ethylbenzoic acid, and phenylacetic acid;aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinicacid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaicacid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylicacid, tetradecanedioic acid, pentadecanedioic acid, and octadecanedioicacid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid;and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid,terephthalic acid, and naphthalenedicarboxylic acid.

Specific examples of the amine compound include, but are notparticularly limited to, the following: aliphatic monoamines such asbutylamine, pentylamine, hexylamine, heptylamine, octylamine,2-ethylhexylamine, nonylamine, decylamine, undecylamine, dodecylamine,tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine,octadecylamine, nonadecylamine, and icosylamine; alicyclic monoaminessuch as cyclohexylamine and methylcyclohexylamine; aromatic monoaminessuch as benzylamine and B-phenylethylamine; aliphatic diamines such as1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane,1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane,1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane,1,13-diaminotridecane, 1,14-diaminotetradecane, 1,15-diaminopentadecane,1,16-diaminohexadecane, 1,17-diaminoheptadecane, 1,18-diaminooctadecane,1,19-diaminononadecane, and 1,20-diaminoeicosane; alicyclic diaminessuch as cyclohexanediamine and bis-(4-aminohexyl)methane, and aromaticdiamines such as xylylenediamine.

Although the terminal group concentration of the polyamide-based resinis not particularly limited, the terminal amino group concentration maybe high so as to improve dyeability for the intended use of the fibersand design materials suitable for alloying for intended use of resin.Also, the terminal amino group concentration may be low so as to reducecoloration or gelation under long-term aging conditions. Moreover, boththe terminal carboxyl group concentration and the terminal amino groupconcentration may be low so as to prevent the regeneration of lactamduring remelting, filament breakage during melt spinning due to theformation of oligomers, mold deposit during continuous injectionmolding, and die mark formation during continuous film extrusion. Theterminal group concentration may be adjusted according to the intendeduse, and both the terminal amino group concentration and the terminalcarboxyl group concentration are preferably 1.0×10⁻⁵ to 15.0×10⁻⁵ eq/g,more preferably 2.0×10⁻⁵ to 12.0×10⁻⁵ eq/g, or particularly preferably3.0×10⁻⁵ to 11.0×10⁻⁵ eq/g. In this specification, a numerical rangeindicated by “ . . . to . . . ” includes two end values in a mannersimilar to the numerical range indicated by “ . . . or more and . . . orless”.

There are some methods to add the end-capping agent. For example, theend-capping agent may be (i) added simultaneously with raw materialssuch as caprolactam in the initial stage of polymerization, (ii) addedin the process of polymerization, or (iii) added while the molten nylonresin is passing through a vertical stirring-type thin film evaporator.The end-capping agent may be added as it is, or added after having beendissolved in a small amount of solvent.

The polyamide-based resin composition may contain other resins inaddition to the polyamide-based resin. Examples of the other resinsinclude a vinyl chloride-based resin, a modacrylic-based resin, apolycarbonate-based resin, a polyolefin-based resin, and a polyphenylenesulfide-based resin. Other resins may be used individually or incombinations of two or more.

From the viewpoint of obtaining a texture and an appearance similar tothose of human hair and improving the curl setting properties andcurl-holding properties, the core of the core-sheath conjugate fiber forartificial hair is preferably composed of a polyester-based resincomposition containing, as a main component, at least one polyesterresin selected from the group consisting of polyalkylene terephthalateand a copolyester mainly containing polyalkylene terephthalate, and thesheath thereof is more preferably composed of a polyamide-based resincomposition containing, as a main component, a polyamide-based resinmainly containing at least one selected from the group consisting ofnylon 6 and nylon 66. In an embodiment of the present invention, thewording “polyamide-based resin mainly containing at least one selectedfrom the group consisting of nylon 6 and nylon 66” refers to thepolyamide-based resin containing 80 mol % or more of nylon 6 and/ornylon 66.

In one or more embodiments of the present invention, a resin compositionin the core or the sheath may contain a pigment in order to obtaincore-sheath conjugate fibers for artificial hair having a desired color.There is no particular limitation on the pigment, and ordinary pigmentssuch as carbon black or anthraquinone-based pigments can be used, forexample. Pigment masterbatch can also be used. A “pigment masterbatch”is obtained by kneading a pigment and a resin composition using akneading machine such as an extruder and pelletizing (also referred toas compounding) the resulting mixture, and pigments, which are usuallyconsidered to be difficult to handle because the pigments are in thefine powder form, can be easily handled by pre-dispersing a pigment in aresin composition, which can suppress uneven coloring of the fibers tobe obtained.

The amount of the pigment added to the polyester-based resin compositionthat constitutes the core is, but is not particularly limited to,preferably 0.005 parts by weight or more and 2 parts by weight or less,and more preferably 0.01 parts by weight or more and 1 part by weight orless, with respect to 100 parts by weight of the polyester-based resin.Further, the amount of the pigment added to the polyamide-based resincomposition that constitutes the sheath is, but is not particularlylimited to, preferably 0.005 parts by weight or more and 2 parts byweight or less, and more preferably 0.01 parts by weight or more and 1part by weight or less, with respect to 100 parts by weight of thepolyamide-based resin.

In one or more embodiments of the present invention, a flame retardantmay be used in combination from the viewpoint of flame resistance.Examples of the flame retardant include bromine-containing flameretardants and phosphorus-containing flame retardants. Examples of thephosphorus-containing flame retardant include phosphoric acid esteramide compounds and organic cyclic phosphorus-based compounds. Examplesof the bromine-based flame retardant include, but are not particularlylimited to the following: a brominated epoxy-based flame retardant;bromine-containing phosphate esters such as pentabromotoluene,hexabromobenzene, decabromodiphenyl, decabromodiphenyl ether,bis(tribromophenoxy)ethane, tetrabromophthalic anhydride, ethylenebis(tetrabromophthalimide), ethylene bis(pentabromophenyl),octabromotrimethylphenylindan, and tris(tribromoneopentyl)phosphate;brominated polystyrenes; brominated polybenzyl acrylates; brominatedphenoxy resins; brominated polycarbonate oligomers; tetrabromobisphenolA and tetrabromobisphenol A derivatives such as tetrabromobisphenolA-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(allyl ether),and tetrabromobisphenol A-bis(hydroxyethyl ether); bromine-containingtriazine compounds such as tris(tribromophenoxy)triazine; andbromine-containing isocyanuric acid compounds such astris(2,3-dibromopropyl)isocyanurate. In particular, the brominatedepoxy-based flame retardant is preferred in terms of heat resistance andflame resistance.

The brominated epoxy-based flame retardant may have an epoxy group ortribromophenol at the end of the molecule as a raw material. Thestructure of the brominated epoxy-based flame retardant after meltkneading is not particularly limited, and preferably has 80 mol % ormore of a constitutional unit represented by the following chemicalformula (1), where the total number of the constitutional unitrepresented by the chemical formula (1) and other constitutional unitsin which at least a part of the chemical formula (1) has been modifiedis taken as 100 mol %. The structure at the end of the molecule of thebrominated epoxy-based flame retardant may be changed after meltkneading. For example, the end of the molecule of the brominatedepoxy-based flame retardant may be replaced by groups other than theepoxy group or tribromophenol, such as a hydroxyl group, a phosphoricacid group, and a phosphonic acid group. Alternatively, the end of themolecule of the brominated epoxy-based flame retardant may be bound to apolyester component through an ester group.

Apart of the structure of the brominated epoxy-based flame retardant,except for the end of the molecule, may also be changed. For example,the secondary hydroxyl group and the epoxy group of the brominatedepoxy-based flame retardant may be bound together to form a branchedstructure. Moreover, a part of the bromine of the chemical formula (1)may be eliminated or added if the bromine content in the molecule of thebrominated epoxy-based flame retardant is not significantly changed.

The brominated epoxy-based flame retardant may be, e.g., a polymericbrominated epoxy-based flame retardant as represented by the followinggeneral formula (2). In the general formula (2), m is 1 to 1000. Thepolymeric brominated epoxy-based flame retardant represented by thegeneral formula (2) may be a commercially available product such as abrominated epoxy-based flame retardant (trade name “SR-T2MP”)manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.

The content of the brominated epoxy flame retardant in the core and/orthe sheath is, but is not particularly limited to, 5 parts by weight ormore and 40 parts by weight or less with respect to 100 parts by weightof the main component resin, for example. From the viewpoint of heatresistance and flame resistance, for example, it is preferable that thecore is composed of a polyester-based resin composition containing atleast one polyester resin selected from the group consisting ofpolyalkylene terephthalate and a copolyester mainly containingpolyalkylene terephthalate in an amount of 100 parts by weight and abrominated epoxy flame retardant in an amount of 5 parts by weight ormore and 40 parts by weight or less, and the sheath is composed of apolyamide-based resin composition containing a polyamide-based resinmainly containing at least one selected from the group consisting ofnylon 6 and nylon 66 in an amount of 100 parts by weight and abrominated epoxy flame retardant in an amount of 5 parts by weight ormore and 40 parts by weight or less.

In one or more embodiments of the present invention, a flame retardantauxiliary may be used in combination. The flame retardant auxiliary isnot particularly limited, and from the viewpoint of flame resistance, itis preferable to use an antimony-based compound or a composite metalcontaining antimony, for example. Examples of the antimony-basedcompound include antimony trioxide, antimony tetroxide, antimonypentoxide, sodium antimonate, potassium antimonate, and calciumantimonate. In terms of the effects of the flame retardant auxiliary onthe flame resistance and the texture, it is more preferable that theflame retardant auxiliary may be at least one selected from the groupconsisting of antimony trioxide, antimony pentoxide, and sodiumantimonate.

The content of the flame retardant auxiliary in the core and/or thesheath is preferably; but is not particularly limited to, 0.1 parts byweight or more and 10 parts by weight or less with respect to 100 partsby weight of the main component resin, for example.

In particular, as a result of adding a flame retardant auxiliary to thepolyamide-based resin composition that constitutes the sheath, anappropriate surface unevenness is formed on the fiber surface, thusobtaining core-sheath conjugate fibers for artificial hair having flameresistance, and a low gross and an appearance that are similar to thoseof human hair.

The core-sheath conjugate fibers for artificial hair may contain variousadditives as needed, to the extent that they do not interfere with thepurpose of one or more embodiments of the present invention. Theadditives include, e.g., a heat-resistant agent, a stabilizer, afluorescent agent, an antioxidant, and an antistatic agent.

The core-sheath conjugate fibers for artificial hair can be produced bymelt kneading the resin compositions respectively for the core and thesheath using various ordinary kneading machines, and melt spinning theresulting composition using a core-sheath conjugate nozzle. A corecomponent is prepared by melt kneading, using various ordinary kneadingmachines, a polyester-based resin composition obtained by dry-blendingthe above-described components such as the polyester resin and thebrominated epoxy-based flame retardant, whereas a sheath component isprepared by melt kneading, using various ordinary kneading machines, apolyamide-based resin composition obtained by dry-blending theabove-described components such as the polyamide-based resin, thepigment, and the brominated epoxy-based flame retardant, and then thecore-sheath conjugate fibers for artificial hair can be produced by meltspinning the core component and the sheath component using a core-sheathconjugate spinning nozzle, for example. Examples of the kneading machineinclude a single-screw extruder, a twin-screw extruder, a roll, aBanbury mixer, and a kneader. In particular, the twin-screw extruder ispreferred in terms of the adjustment of the degree of kneading and easeof operation.

As the method for producing the fiber of the present invention, it ispreferable to use a melt spinning method, and, for example, in the caseof a polyester-based resin composition, melt spinning is performed whilethe temperatures of an extruder, a gear pump, a nozzle, and the like areset to 250° C. or more and 300° C. or less, and in the case of apolyamide-based resin composition, melt spinning is performed while thetemperatures of an extruder, a gear pump, a nozzle, and the like are setto 260° C. or more and 320° C. or less, after which the extruded yarnsare cooled to a temperature of not more than the glass transition pointof the corresponding resin, and wound up at a speed of 30 m/min or moreand 5000 m/min or less, and thus melt spun yarns (undrawn yarns) areobtained.

Specifically, during the melt spinning, the polyester-based resincomposition for constituting the core is supplied from a core extruderof a melt spinning machine, the polyamide-based resin composition forconstituting the sheath is supplied from a sheath extruder of the meltspinning machine, and the molten polymer is extruded through acore-sheath type conjugate spinning nozzle (holes) with a predeterminedshape, and thus the melt spun yarns (undrawn yarns) are obtained. It ispreferable that the melt spun yarns (undrawn yarns) are hot drawn. Thedrawing may be performed by either a two-step method or a directspinning-drawing method. In the two-step method, the melt spun yarns areonce wound, and then drawn. In the direct spinning-drawing method, themelt spun yarns are drawn continuously without winding. The hot drawingmay be performed by a single-stage drawing method or a multi-stagedrawing method that includes two or more stages.

The heating means in the hot drawing may be, e.g., a heating roller, aheat plate, a steam jet apparatus, or a hot water bath, and they can beused in combination as appropriate.

Oils such as a fiber treatment agent and a softening agent may beapplied to the core-sheath conjugate fibers for artificial hair to makethe texture and feel of the fibers more similar to human hair. The fibertreatment agent may be, e.g., a silicone-based fiber treatment agent ora non-silicone-based fiber treatment agent used to improve the textureand combing property of the fibers.

The core-sheath conjugate fibers for artificial hair may be subjected togear crimping. The gear crimping imparts gentle curves and naturalappearance to the fibers, and also reduces the adhesion between thefibers, thereby also improving the combing property.

In the gear crimping, the fibers are generally heated to a temperaturehigher than the softening temperature and allowed to pass through twoengaged gears so that the shape of the gears is transferred to thefibers. This can create curls on the fibers.

Also, in the fiber processing stage, if necessary, curls havingdifferent shapes can be created by heating the core-sheath conjugatefibers for artificial hair at different temperatures.

(Hair Ornaments)

In one or more embodiments of the present invention, the core-sheathconjugate fibers for artificial hair can be used as artificial haireither individually or can be used in combination with other artificialhair fibers and natural fibers such as human hair and animal hair.Examples of the other artificial hair fibers include acrylic fibers.

In one or more embodiments of the present invention, the core-sheathconjugate fibers for artificial hair may be used without particularlimitation as long as they are used for hair ornaments. The core-sheathconjugate fibers for artificial hair may be used for hair wigs,hairpieces, weaving hair hair extensions, braided hair, hairaccessories, and doll hair.

The hair ornaments may include only the core-sheath conjugate fibers forartificial hair of one or more embodiments of the present invention.Alternatively, the hair ornaments may include the core-sheath conjugatefibers for artificial hair of the present invention in combination withother artificial hair fibers and natural fibers such as human hair andanimal hair.

EXAMPLES

Hereinafter, one or more embodiments of the present invention will bedescribed in more detail by way of examples. However, one or moreembodiments of the present invention are not limited to the followingexamples.

The measurement methods and the evaluation methods used in Examples andComparative Examples are as follows.

(Single Fiber Fineness)

Using an auto-vibronic fineness measuring device “DENIER COMPUTER DC-11”(manufactured by Search Co., Ltd), 30 samples were measured to determinetheir respective single fiber fineness, and the average of the measuredvalues of the samples was calculated and taken as the single fiberfineness of the core-sheath conjugate fibers.

(Evaluation of Fiber Cross-Section)

At room temperature (23° C.), fibers were cut to a length of 150 mm and0.7 g of the cut fibers were bundled, inserted into a rubber tube, andheated at 80° C. so as to shrink the tube such that the fiber bundle wasfixed so as not to be displaced. Thereafter, a portion of the tube wascut using a cutter, and thus a fiber bundle for cross-sectionobservation having a length of 5 mm was prepared. An image of this fiberbundle was captured using a laser microscope (“VK-9500” manufactured byKeyence Corporation) at a magnification of 400 times, and thus aphotograph of fiber cross-sections was obtained. A core-to-sheath arearatio was calculated based on the fiber cross-section photograph. Also,fiber cross-sections of thirty fibers were selected at random from thisfiber cross-section photograph, and the length of the major axes of thefiber cross-sections, the length of first minor axes of the fibercross-sections, the length of the major axes of the core cross-sections,the length of the first minor axes of the core cross-sections, and thetwo-point distance between the center point of the first minor axes ofthe fiber cross-sections and the center point of the first minor axes ofthe core cross-sections were measured. Note that, in the core-sheathconjugate fibers for artificial hair according to an embodiment of thepresent invention, values such as the length of the major axis of thefiber cross-section, the length of the first minor axis of the fibercross-section, the length of the major axis of the core cross-section,the length of the first minor axis of the core cross-section, thetwo-point distance between the center point of the first minor axis ofthe fiber cross-section and the center point of the first minor axis ofthe core cross-section, a ratio between the length of major axis of thefiber cross-section and the length of the first minor axis of the fibercross-section, and a ratio between the length of the major axis of thecore cross-section and the length of the first minor axis of the corecross-section can be indicated using the corresponding average value ofthe measured values of the fiber cross-sections of the thirty fibers,which were selected at random.

(Texture)

Sensory evaluation was performed by a professional cosmetologist, andthe texture was evaluated in the following four stages.

-   -   A: The texture is very good and equivalent to that of human        hair.    -   B: The texture is good, but slightly inferior to that of human        hair.    -   C: The texture is good, but inferior to that of human hair.    -   D: The texture is poor and significantly inferior to that of        human hair.

(Appearance)

Sensory evaluation was performed by a professional cosmetologist, andthe appearance was evaluated in the following four stages.

-   -   A The appearance is natural appearance equivalent to that of        human hair.    -   B: The appearance is natural appearance, but slightly inferior        to that of human hair.    -   C: The appearance is natural appearance, but inferior to that of        human hair.    -   D: The appearance is unnatural appearance and significantly        inferior to that of human hair.

(Curl Setting Properties)

2.8 g of filaments were formed into a hair tress with a length of 25 cmand wrapped around a pipe with a diameter of 32 mm at room temperature(23° C.), curled at 120° C. for 60 minutes, and aged at room temperature(23° C.) for 60 minutes. Thereafter, one end of the curled filaments wasfixed and suspended, and the length of the curled filaments wasmeasured. The curl setting properties were evaluated using the filamentlength as an index for curl setting properties in the following fourstages.

-   -   A: The length of the curled filaments is less than 13 cm.    -   B: The length of the curled filaments is 13 cm or more and less        than 15 cm.    -   C: The length of the curled filaments is 15 cm or more and less        than 17 cm.    -   D: The length of the curled filaments is 17 cm or more.

Example 1

First, 100 parts by weight of polyethylene terephthalate pellets(EastPET trade name “A-12”, which is referred to as PET, manufactured byEast West Chemical Private Limited) were mixed with 30 parts by weigh ofa brominated epoxy-based flame retardant (trade name “SR-T2MP”manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.), 3 parts by weight ofsodium antimonate (trade name “SA-A” manufactured by Nihon Seiko Co.,Ltd.), 3.0 parts by weight of black pigment masterbatch (trade name“PESM 22367 BLACK (20)” manufactured by Dainichiseika Color & ChemicalsMfg. Co., Ltd., pigment: 20% by weight, base resin: polyester-basedresin), 0.6 parts by weight of yellow pigment masterbatch (trade name“PESM 1001 YELLOW (20)” manufactured by Dainichiseika Color & ChemicalsMfg. Co., Ltd., pigment: 20% by weight, base resin: polyester-basedresin), and 0.2 parts by weight of red pigment masterbatch (trade name“PESM 3005 RED (20%) manufactured by Dainichiseika Color & ChemicalsMfg. Co., Ltd., pigment: 20% by weight, base resin: polyester-basedresin). The mixture was dry blended and then fed into a twin-screwextruder, where it was melt-kneaded at a barrel temperature of 280° C.and pelletized. Thus, a polyester-based resin composition was obtained.

Then, 100 parts by weight of nylon 6 (also referred to as PA) (tradename “A1030BRL” manufactured by Unitika Ltd.) were mixed with 12 partsby weight of a brominated epoxy-based flame retardant (trade name“SR-T2MP manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.), 2 parts byweight of sodium antimonate (trade name “SA-A” manufactured by NihonSeiko Co., Ltd.), 2.0 parts by weight of black pigment masterbatch(trade name “PAM (F) 25005 BLACK (20)” manufactured by DainichiseikaColor & Chemicals Mfg. Co., Ltd.), 0.8 parts by weight of yellow pigmentmasterbatch (trade name “PAM (F) 28990 YELLOW (20)” manufactured byDainichiseika Color & Chemicals Mfg. Co., Ltd.), and 0.5 parts by weightof red pigment masterbatch (trade name “PAM (F) 28991 RED (20)”manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.). Themixture was dry blended and then fed into a twin-screw extruder, whereit was melt-kneaded at a barrel temperature of 260° C. and pelletized.Thus, a polyamide-based resin composition was obtained.

Next, the polyester-based resin composition in the form of pellets andthe polyamide-based resin composition in the form of pellets were fedinto extruders, respectively; and then extruded through a core-sheathtype conjugate spinning nozzle having a nozzle shape shown in Table 1below at a set temperature of 270° C. and wound up at a speed of 40 to200 m/min. This resulted in undrawn yarns of core-sheath conjugatefibers containing the polyester-based resin composition as a core andthe polyamide-based resin composition as a sheath and having acore-to-sheath area ratio of 5:5.

The undrawn yarns thus obtained were drawn to 3 times and taken up at aspeed of 45 m/min by using a heating roller at 85° C. Subsequently, thedrawn yarns were further heat-treated and wound up at a speed of 45m/min by using a heating roller at 200° C. A polyether oil (trade name“KWC-Q” manufactured by Marubishi Oil Chemical Corporation) was appliedto the drawn yarns so that the amount of oil applied was 0.20% omf(i.e., the weight percentage of the oil (pure content) with respect tothe dry fiber weight). Then, the resulting yarns were dried, and thuscore-sheath conjugate fibers with a single fiber fineness shown in Table1 below and an eccentricity ratio of 15.6% in the minor axis directionwere obtained.

Example 2

Core-sheath conjugate fibers were produced in the same manner as Example1 except that a core-sheath type conjugate spinning nozzle having thenozzle shape shown in Table 1 below was used, the eccentricity ratio inthe minor axis direction was 12.7% and the core-to-sheath area ratio was6:4.

Example 3

Core-sheath conjugate fibers were produced in the same manner as Example1 except that the resin used for the sheath was changed to nylon 66(also referred to as “PA66”) (trade name “Amilan CM3001” manufactured byToray Industries, Inc.), the barrel temperature was set to 280° C.during pelletization, the nozzle temperature was set to 280° C., theeccentricity ratio in the minor axis direction was 15.1%, and thecore-to-sheath area ratio was 3:7.

Example 4

Core-sheath conjugate fibers were produced in the same manner as Example1 except that a core-sheath type conjugate spinning nozzle having thenozzle shape shown in Table 1 below was used, the resin used for thecore was changed to polybutylene terephthalate (also referred to as“PBT”) (trade name “Novaduran 5020” manufactured by Mitsubishi ChemicalCorporation), the barrel temperature was set to 260° C. duringpelletization, the nozzle temperature was set to 260° C., theeccentricity ratio in the minor axis direction was 6.8%, and thecore-to-sheath area ratio was 7:3.

Comparative Example 1

Core-sheath conjugate fibers were produced in the same manner as Example1 except that a core-sheath type conjugate spinning nozzle having thenozzle shape shown in Table 1 below was used, and the eccentricity ratioin the minor axis direction was 0%.

Comparative Example 2

Core-sheath conjugate fibers were produced in the same manner as Example1 except that the eccentricity ratio in the minor axis direction was14.1% and the core-to-sheath area ratio was 1:9.

Comparative Example 3

Core-sheath conjugate fibers were produced in the same manner as Example1 except that a core-sheath type conjugate spinning nozzle having thenozzle shape shown in Table 1 below was used, the eccentricity ratio inthe minor axis direction was 2.4% and the core-to-sheath area ratio was8:2.

Comparative Example 4

Core-sheath conjugate fibers were produced in the same manner as Example1 except that a core-sheath type conjugate spinning nozzle having thenozzle shape shown in Table 1 below was used, and the eccentricity ratioin the minor axis direction was 9.3%.

The cross-sectional shapes of the fibers of the examples and comparativeexamples were evaluated and observed as described above. Furthermore,the texture, appearance, and the curl setting properties of the fibersof the examples and comparative examples were evaluated as describedabove. Table 1 shows the results.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3Comp. Ex. 4 Nozzle shape (fiber) flat bilobed flat bilobed flat bilobedflat bilobed flat bilobed flat bilobed flat bilobed circular Nozzleshape (core) elliptical flat bilobed elliptical flat bilobed flatbilobed elliptical flat bilobed circular Main component resin (core) PETPET PET PBT PET PET PET PET Main component resin (sheath) PA6 PA6 PA66PA6 PA6 PA6 PA6 PA6 Core-to-sheath area ratio 5:5 6:4 3:7 7:3 5:5 1:98:2 5:5 Single fiber fineness (dtex) 58 59 56 60 62 54 57 60Cross-sectional shape (fiber) flat bilobed flat bilobed flat bilobedflat bilobed flat bilobed flat bilobed flat bilobed circularCross-sectional shape (core) elliptical flat bilobed elliptical flatbilobed flat bilobed elliptical flat bilobed circular L/S1 1.5 1.5 1.41.4 1.4 1.5 1.4 1.0 Lc/Sc1 1.6 1.7 1.5 1.5 1.6 1.6 1.5 1.0 Eccentricityratio (%) 15.6 12.7 15.1 6.8 0 14.1 2.4 9.3 Photograph of cross-sectionFIG. 2 — — — FIG. 3 — — — Texture A B B C A C D D Appearance B B A C B BD D Curl setting properties B B A B D D B B

FIG. 2 is a laser microscopic photograph of cross-sections of the fibersof Example 1. As can be seen from FIG. 2 , in the core-sheath conjugatefibers for artificial hair of Example 1, the fibers had a flat bilobedcross-sectional shape, the core had an elliptical cross-sectional shape,the major axis of the core cross-section is in a direction thatsubstantially coincides with a direction of the major axis of the fibercross-section, and the fibers were eccentric in the minor axisdirection.

FIG. 3 is a laser microscopic photograph of cross-sections of the fibersof Comparative Example 1. As illustrated in FIG. 3 , in the core-sheathconjugate fibers for artificial hair of Comparative Example 1, thefibers and the cores had a flat bilobed cross-sectional shape, the majoraxis of the core cross-section is in a direction that substantiallycoincides with a direction of the major axis of the fiber cross-section,but the fibers were not eccentric in the minor axis direction.

As can be seen from Table 1, the fibers of Examples 1 to 4 had a textureand an appearance that are similar to those of human hair, and favorablecurl setting properties.

On the other hand, the fibers of Comparative Example 1 having aneccentricity ratio of 0% and the fibers of Comparative Example 2 havinga high sheath ratio had poor curl setting properties. Cores of thefibers of Comparative Example 3 having a high core ratio were exposedfrom the fiber surface, and the fibers of Comparative Example 3 had verybad texture and appearance, and thus was not formed as good fibers. Thefibers of Comparative Example 4 had a circular fiber cross-sectionalshape and a circular core cross-sectional shape, resulting in anunnatural appearance and a bad texture.

One or more embodiments of the present invention preferably include atleast the following embodiments, but are not limited thereto.

[1] A core-sheath conjugate fiber for artificial hair comprising:

-   -   a core; and    -   a sheath,    -   wherein the core is composed of a polyester-based resin        composition containing a polyester-based resin as a main        component, and the sheath is composed of a polyamide-based resin        composition containing a polyamide-based resin as a main        component, and    -   a core-to-sheath area ratio of the core to the sheath is 2:8 to        7:3, and both a fiber cross-section and a core cross-section        have a flat shape, a major axis of the core cross-section is in        a direction that substantially coincides with a direction of a        major axis of the fiber cross-section, and an eccentricity ratio        of the fiber in a minor axis direction is 5% or more.

[2] The core-sheath conjugate fiber for artificial hair according to[1], wherein the fiber cross-section has a flat multilobed shape.

[3] The core-sheath conjugate fiber for artificial hair according to [1]or [2], wherein the core cross-section has an elliptical or flatmultilobed shape.

[4] The core-sheath conjugate fiber for artificial hair according to anyone of [1] to [3], wherein a length of the major axis of the fibercross-section and a length of a first minor axis of the fibercross-section satisfy the equation (1) below, where the major axis ofthe fiber cross-section is a longest straight line among an axisymmetricaxis and straight lines connecting any two points on the outercircumference of the fiber cross-section so as to be parallel to theaxisymmetric axis, and the first minor axis of the fiber cross-sectionis a longest straight line formed when any two points on the outercircumference of the fiber cross-section are connected perpendicularlyto the major axis of the fiber cross-section,

the length of the major axis of the fiber cross-section/the length ofthe first minor axis of the fiber cross-section=1.1 or more and 2.0 orless  (1).

[5] The core-sheath conjugate fiber for artificial hair according to anyone of [1] to [4], wherein a length of the major axis of the corecross-section and a length of a first minor axis of the corecross-section satisfy the equation (2) below, where the major axis ofthe core cross-section is a longest straight line among an axisymmetricaxis and straight lines connecting any two points on the outercircumference of the core cross-section so as to be parallel to theaxisymmetric axis, and the first minor axis of the core cross-section isa longest straight line formed when any two points on the outercircumference of the core cross-section are connected perpendicularly tothe major axis of the core cross-section,

the length of the major axis of the core cross-section/the length of thefirst minor axis of the core cross-section=1.3 or more and 2.0 orless  (2).

[6] The core-sheath conjugate fiber for artificial hair according to anyone of [1]to [5], wherein the polyester-based resin composition containsat least one polyester-based resin selected from the group consisting ofpolyalkylene terephthalate and a copolyester mainly containingpolyalkylene terephthalate.

[7] The core-sheath conjugate fiber for artificial hair according to anyone of [1] to [6], wherein the polyamide-based resin compositioncontains a polyamide-based resin mainly containing at least one selectedfrom the group consisting of nylon 6 and nylon 66.

[8] A hair ornament comprising the core-sheath conjugate fiber forartificial hair according to any one of [1] to [7].

[9] The hair ornament according to [8], wherein the hair ornament is anyone selected from the group consisting of a hair wig, a hairpiece,weaving hair, a hair extension, braided hair, a hair accessory, and dollhair.

[10]A method for producing the core-sheath conjugate fiber forartificial hair according to any one of [1] to [7], comprising:

-   -   melt spinning a polyester-based resin composition and a        polyamide-based resin composition, using a core-sheath conjugate        nozzle,    -   wherein both a fiber cross-section and a core cross-section of        the core-sheath conjugate fiber for artificial hair have a flat        shape, a major axis of the core cross-section is in a direction        that substantially coincides with a direction of a major axis of        the fiber cross-section, and an eccentricity ratio of the fiber        in a minor axis direction is 5% or more.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 Core-sheath conjugate fiber for artificial hair        (cross-section)    -   10 Sheath    -   11 Major axis of the fiber cross-section    -   12 First minor axis of the fiber cross-section    -   13 Center point of first minor axis of the fiber cross-section    -   20 Core    -   21 Major axis of the core cross-section    -   22 First minor axis of the core cross-section    -   23 Center point of first minor axis of the core cross-section

1. A core-sheath conjugate fiber for artificial hair comprising: a core;and a sheath, wherein the core comprises a polyester-based resincomposition comprising a polyester-based resin, and the sheath comprisesa polyamide-based resin composition comprising a polyamide-based resin,and a core-to-sheath area ratio of an area of the core to an area of thesheath is 2:8 to 7:3, both a fiber cross-section and a corecross-section have a flat shape, a major axis of the core cross-sectionis in a direction that substantially coincides with a direction of amajor axis of the fiber cross-section, and an eccentricity ratio of thefiber in a minor axis direction is 5% or more.
 2. The core-sheathconjugate fiber for artificial hair according to claim 1, wherein thefiber cross-section has a flat multilobed shape.
 3. The core-sheathconjugate fiber for artificial hair according to claim 1, wherein thecore cross-section has an elliptical or flat multilobed shape.
 4. Thecore-sheath conjugate fiber for artificial hair according to claim 1,wherein a length of the major axis of the fiber cross-section and alength of a first minor axis of the fiber cross-section satisfy theequation (1) below, where the major axis of the fiber cross-section is alongest straight line among an axisymmetric axis and straight linesconnecting any two points on the outer circumference of the fibercross-section so as to be parallel to the axisymmetric axis, and thefirst minor axis of the fiber cross-section is a longest straight lineformed when any two points on the outer circumference of the fibercross-section are connected perpendicularly to the major axis of thefiber cross-section,the length of the major axis of the fiber cross-section/the length ofthe first minor axis of the fiber cross-section=1.1 or more and 2.0 orless  (1).
 5. The core-sheath conjugate fiber for artificial hairaccording to claim 1, wherein a length of the major axis of the corecross-section and a length of a first minor axis of the corecross-section satisfy the equation (2) below, where the major axis ofthe core cross-section is a longest straight line among an axisymmetricaxis and straight lines connecting any two points on the outercircumference of the core cross-section so as to be parallel to theaxisymmetric axis, and the first minor axis of the core cross-section isa longest straight line formed when any two points on the outercircumference of the core cross-section are connected perpendicularly tothe major axis of the core cross-section,the length of the major axis of the core cross-section/the length of thefirst minor axis of the core cross-section=1.3 or more and 2.0 orless  (2).
 6. The core-sheath conjugate fiber for artificial hairaccording to claim 1, wherein the polyester-based resin compositioncomprises at least one polyester-based resin selected from the groupconsisting of polyalkylene terephthalate and a copolyester comprising 80mol % or more of polyalkylene terephthalate.
 7. The core-sheathconjugate fiber for artificial hair according to claim 1, wherein thepolyamide-based resin composition comprises a polyamide-based resincomprising at least 80 mol % or more of one selected from the groupconsisting of nylon 6 and nylon
 66. 8. A hair ornament comprising thecore-sheath conjugate fiber for artificial hair according to claim
 1. 9.The hair ornament according to claim 8, wherein the hair ornament is atleast one selected from the group consisting of a hair wig, a hairpiece,weaving hair, a hair extension, braided hair, a hair accessory, and dollhair.
 10. A method for producing the core-sheath conjugate fiber forartificial hair according to claim 1, comprising: melt spinning apolyester-based resin composition and a polyamide-based resincomposition, using a core-sheath conjugate nozzle, wherein both a fibercross-section and a core cross-section of the core-sheath conjugatefiber for artificial hair have a flat shape, a major axis of the corecross-section is in a direction that substantially coincides with adirection of a major axis of the fiber cross-section, and aneccentricity ratio of the fiber in a minor axis direction is 5% or more.11. The hair ornament according to claim 8, wherein the fibercross-section has a flat multilobed shape.
 12. The hair ornamentaccording to claim 8, wherein the core cross-section has an ellipticalor flat multilobed shape.
 13. The hair ornament according to claim 8,wherein a length of the major axis of the fiber cross-section and alength of a first minor axis of the fiber cross-section satisfy theequation (1) below, where the major axis of the fiber cross-section is alongest straight line among an axisymmetric axis and straight linesconnecting any two points on the outer circumference of the fibercross-section so as to be parallel to the axisymmetric axis, and thefirst minor axis of the fiber cross-section is a longest straight lineformed when any two points on the outer circumference of the fibercross-section are connected perpendicularly to the major axis of thefiber cross-section,the length of the major axis of the fiber cross-section/the length ofthe first minor axis of the fiber cross-section=1.1 or more and 2.0 orless  (1).
 14. The hair ornament according to claim 8, wherein a lengthof the major axis of the core cross-section and a length of a firstminor axis of the core cross-section satisfy the equation (2) below,where the major axis of the core cross-section is a longest straightline among an axisymmetric axis and straight lines connecting any twopoints on the outer circumference of the core cross-section so as to beparallel to the axisymmetric axis, and the first minor axis of the corecross-section is a longest straight line formed when any two points onthe outer circumference of the core cross-section are connectedperpendicularly to the major axis of the core cross-section,the length of the major axis of the core cross-section/the length of thefirst minor axis of the core cross-section=1.3 or more and 2.0 orless  (2).
 15. The hair ornament according to claim 8, wherein thepolyester-based resin composition comprises at least one polyester-basedresin selected from the group consisting of polyalkylene terephthalateand a copolyester comprising 80 mol % or more of polyalkyleneterephthalate.
 16. The hair ornament according to claim 8, wherein thepolyamide-based resin composition comprises a polyamide-based resincomprising 80 mol % or more of at least one selected from the groupconsisting of nylon 6 and nylon 66.